1. Field of the Invention
The invention concerns a system for determining the absolute torque applied to a rotating shaft, in particular the shaft of a vehicle steering column. The invention also concerns a module for measuring the torque applied to the rotating shaft comprising such a system.
2. Description of Related Art
A conventional steering column is composed of a tubular sheath fixed to the bodywork of the vehicle, guiding and supporting a steering shaft. The steering shaft connects the steering wheel to the steered wheels of the vehicle.
In a variant, the invention also applies to decoupled steering systems in which the steering column does not provide a direct mechanical connection between the steering wheel and the wheels. This is because, unlike conventional steering columns, decoupled steering columns are not associated with a steering box converting the circular movement of the steering wheel into an angular movement of the steering arm which causes the wheels to turn.
The torque measurement on the steering shaft is necessary in particular in electrical assisted steering systems since the triggering of the assistance depends in particular on the torque applied by the driver to the steering wheel.
The torque measuring device used in electrical assisted steering systems emits a signal indicating the torque exerted by the driver on the steering wheel and therefore on the vehicle steering shaft.
This signal is conventionally sent to a steering assistance computer which triggers the assistance, controlling for example an electric motor, in the case of electrical assisted steering.
Measurement of the torque applied to the steering wheel can also be used, for example, in simulators in order to provide, in real time, good simulation of driving.
This is because the restoration of forces at the steering wheel by virtue of a mechanism generating a torque on the steering wheel according to the type of vehicle to be simulated, equipped or not with assisted steering, must take account of the running conditions to be recreated.
The invention can also apply to other fields such as that of the transmission of forces, for example to the wheels of a vehicle, or to controlling the braking of the said vehicle by means of measuring the torque applied.
There is known, in particular from the document FR-2 816 051 issuing from the applicant, a device for determining the torque applied to a rotating shaft. Such a device has many advantages and makes it possible in particular to simplify the installation. This is because the use of digital sensors dispenses with any variations in air gap and differences in temperature magnitudes.
This type of device makes it possible to determine the relative or absolute torque applied to a rotating shaft.
Relative torque means the value of the torque at a given moment with respect to an arbitrary torque value taken as a reference. This reference value of the torque may then vary from one measurement to another.